Drugs are biologically and psychologically addictive. Stuff like ivory have social appeal. The only reason they are valuable (like diamonds) is because others

Drugs are biologically and psychologically addictive. Stuff like ivory have social appeal. The only reason they are valuable (like diamonds) is because others think they are valuable. So having celebrities decry them hits them directly at their source of appeal unlike drugs. This doesn't affect the bs medicinal market directly but if it reduces the value but keeps the cost high anyways (thanks to additional penalties) it may make the medicines less appealing to those who are price conscious. Of course this is discrimination against the poor and could be a genuine issue if they had real medicinal value but since they actually don't it's much more defensible.